1. Field of the Invention
The invention concerns the field of image display, notably for high-resolution display devices using projectors or back projectors forming the images on a screen or display tubes, and the object of this invention is more particularly a process, and the corresponding device, for image display with automatic defect correction by feedback.
2. Description of the Prior Art
In high-resolution display devices, numerous defects can affect an image, whether it is obtained by projection or back projection on a screen from a monochrome or trichrome tube, or from a set of display tubes.
These defects have many causes (tubes, optical system, electronic parts, movements) and their effects vary with time.
We can list in particular:
geometric defects: the image can be deformed into a barrel-shape around its periphery, for example; PA0 lighting focus defects; PA0 defects of alignment of the three tubes for a trichrome image; PA0 variations with time of these defects. PA0 that it uses for automatic defect correction an image acquisition device which analyses the screen through a spatial filter; the correction involves two successive phases, an acquisition or analysis phase and a correction phase, PA0 that during the acquisition phase, a test image with bright isolated pixels, distributed in the image and with spatially fixed positions, is displayed, the acquisition device being such that as the spatial filter is exactly adapted to the test image, a maximum output signal is detected when a pixel of the test image displayed coincides with its exact position, this acquisition phase including a stage of spatial calibration where the bright pixels of the test image displayed are brought back to their expected positions on the screen, by correction of the horizontal and vertical scanning of the means of display based on the results of image analysis by the acquisition device, the corresponding corrections for the different pixels of the test image being memorized and the corrections for the intermediate pixels being calculated by interpolation from the nearby measured values, PA0 and that during the continuation phase during which the sequence of video images is displayed, the image displayed is analyzed through the spatial filter to update the scanning, focusing and amplitude corrections if necessary and to change their memorized values according to the results of the analysis.
Until now these defects have made it impossible to design an association of several projectors to create a very high-quality image over its whole area, or a very large image of "wall" type by composition of images from different projectors or groups of projectors.